# unit 21 formula presentation 1using formula presentation 2constructing formulae presentation...

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• Unit 21Formula

Presentation 1Using FormulaPresentation 2Constructing FormulaePresentation 3Negative NumbersPresentation 4Temperature DifferencesPresentation 5Substitutions into FormulaePresentation 6More Complex FormulaePresentation 7Changing the SubjectPresentation 8Pendulums

• Unit 21Formula21.1 Using Formula

• Question

What are the perimeter length and area if and?

The perimeter length, P, and area, A, of a rectangle are given by the formulae

where l is the length and w the width of the rectangle.Solution

(b)lw4cm8 cmSolution

(a)????????

• Unit 21Formula21.2 Constructing Formula

• When repairing air conditioning systems, an emergency engineer charges a basic fee of J\$3000 plus J\$1200 per hour.QuestionFind a formula for calculating the engineer's charge for repair work which takes n hours.SolutionLet C = ChargeSo C = fixed charge + hourly charge no. of hours C = J\$3000 + J\$1200 nC = J\$3000 + J\$1200n????QuestionWhat does the engineer charge in total if the repair takes 6 hours?SolutionC = J\$3000 + J\$1200 6C = J\$3000 + J\$7200C = J\$10200?????

• Unit 21Formula21.3 Negative Numbers

• Rules to remember

Calculate

4 + (10) = 66 + 8 = 24 5 = 96 + (7) = 13(40) (5) = 8(24) (3) = 8(40) (5) = 8(6) 7 = 42

????????

-x-=+-x+=-+x-=-+x+=+

--=+-+=-+-=-++=+

• Unit 21Formula21.4 Temperature Differences

• Use information given on the above to answer these questions.What is the difference in temperature between

Kingston and Singapore4Kingston and London25Kingston and Vancouver29London and New York3London and Sydney26Lima and Kingston0Oslo and Kingston30Moscow and Kingston34????????

• Unit 21Formula21.5 Substitution in Formula

• l = (40 + 0.02T) cmThe length of a metal rod changes with temperature according to formula above; where T is the temperature in CQuestionWhat is the length of the rod when(a) T = 50C(b) T = 10C

(a)l = (40 + 0.02 x 50) cm = (40 + 1) cm = 41cmSolution??

(b)l = (40 + 0.02 x 10) cm = (40 + 0.2) cm = 39.8cm????

• Unit 21Formula21.6 More Complex Formula

• The formulagives the focal

length f for a lensQuestion What is the value of f, if u = 10cm and v = 8cm

Solution ?????Hence

?

• Unit 21Formula21.7 Changing the Subject

• The formula that connects Celsius (C) and

Fahrenheit (F) is

Question

Rewrite the formula in the form C = ......Solution

Take 32 from both sides of the formulaMultiply by 5throughout

?

?Divide by 9throughout

?

So

• Unit 21Formula21.8 Pendulums

• Problem

Make l the subject of this equation.

?The period of revolution, T, of a pendulum of length l is given by the formula when G is a constant.

Solution

Divide both sides by to giveSquare both sidesMultiply both sides by G to give???